docs: def get(self, key, namespace=None):
          """Retrieve value for key."""
          if not self.path:
              return NO_VALUE
  
          logger.debug('Searching %r for key: %s, namepsace: %s', self, key, namespace)
          full_key = generate_uppercase_key(key, namespace)
          return get_key_from_envs(self.cfg, full_key)